Method of and apparatus for controlling catalytic processes



J. E. COTTLE Oct. 13, 1959 METHOD 0F AND APPARATUS FOR CONTROLLING CATALYTIC PROCESSES Filed Aug. 25, 1955 2 Sheets-Sheet JOIFZOU NQLMMTN- @maw E J. E. COTTLE oct. 13, 1959 METHOD OF AND APPARATUS FOR CONTROLLING CATALYTIC PROCESSES Filed Aug. 25, 1955 2 Sheets-Sheet 2 f1.9. .mw wlzmw I l A l I INVEN TOR.

` J E coTTLE ORNQS m9 1 ILWM ozjooo n om N@ ow FIIII oma Czmow .65.28 @Haw m1 John E. Cottle, BrtlesvilleyklaL, assigner to Phillips Petroleum Company,.a corporationlof Delaware Application August 2s, 195s, serial No. 530,483 16 Claims; (Cl. 26o-6831s) This invention relates toja method of and apparatus for the control of a catalytic process. A ln liquid phase catalytic processes, it is necessary to separate the unreacted feed from the reaction products. I have discovered that the rate of flow of unreacted feed from this separationstep can be used very advantageously to control the proportions of feed andcatalyst fed to the reaction zone so as to obtain maximum conversion and constanty throughput in thesystern.

The control method and apparatus of the invention are particularly applicable to the liquid phase polymerization of l-olens having. no morethan 8 carbon atoms With-no branching nearer the double bond than the four position, for example,4 ethylene, Where such polymerization takes place in the presence of a granular polymerization catalyst'. t z

. In this process, the polyethylene and-catalyst .are Vseparated from a stream containingsubstantially all the unreacted l-olen in a flash chamber, and` the rate of flow of effluent gasY fromthe. flash system is advantageously utilized, in accordance with the inventiomto control either the rate of flow of oleln to the'reactionzone or the amount of catalyst fed to the reaction zone. l have further found that thejeflectsof fluctuations in this flow rate can be minimized either by, maintaining a constant pressure in the ilash chamber or by integrating a control output representingthe rate of ow of. gaseous material `troduced through a line .havinga motor' valve 20d controlled by a flow recorder controller -20b which has a sensing elementv 20c in theline 20 downstream of the valve 20a. Y

Effluent is withdrawnfrom the reactor through a line 21- which incorporates a valve 22 Yconnected to a pressure controller 23 which has a sensing element 24 disposed within thereactor. This valve regulates the rate of flow of effluent from the reactor so-v as to maintain afconstant predeterminedreactor pressure.v 1 y .M A concentration indicator 24a is connected to theline 21 to show the polymer concentration inthe reactor effluent. f

The eflluent line 21 then passes throughl an indirect heat exchanger 25 and a valved line 26 to a ash chamber 27.

A heating medium enters thefunit 25 through a line 28 in: the line 31 `causes a predetermined level to bemainfrom theflash system overa desired period of time, Y

thus providing aneicient controll action well adapted for commercial operation. i

Accordingly, it is an object of theinvention to provide an improved control system rfor liquidphase reactions conducted in-the presence of a granular catalyst.

Itis a further object to provide an improved `control method for such systems.

It is a still further object to provide a control method and apparatus for the polymerization o-f specilie'd'l-olens and for separation of the polymerizedprodnct from'the unreacted materials. i

Various-.other Objects, advantages and features. of the invention will become apparent from the; following detailed description taken in conjunction with the accompanying drawing, in which: .f A

. Figure lis a oW diagramfof a process Aembodying the control system of this invention;V v

Figure 2, is a block diagram illustrating a featureof the invention; and

Figure 3y is a'flow diagram of a modiedprocess. Referring now to Figure l, l have shown a reactor 410 provided with an agitator orstirrer llfdriven by a motor '12'. Connected tothe reactor 10 isfa feed line 1-3 inf tained inthe vessel 27 by the action of a level controller 31b having Va sensing element in the vessel. A valve 33 is disposedin the line 32, and this valve is connected to a pressure controller 34 having a sensing element 35 in thechamber 27 so that the valve :33 regulates the llow of gas from the chamber 27` to; .maintaina constant pressure therein; Ifl desired the sensing. element 35 can be located in the line 32' upstream of the valve 33.

The gaseous material vfrom the. ash chamber then passesthroughla condenser 36to a separator or knockoutdrum 37 from which liquid is Withdrawn through a line -38' andpassed through pump 39 and a heater 40 to the ilash chamber 27..

An overhead `gas stream is taken from` theV separator to .a line .41, thisl stream containing substantially all the unreacted feed material. i j

In accordance with. the invention, a ow controller'42 has a sensing velement 43 inthe conduit 41 or, if desired, asensing-element 43a in the line 32. j This controller produces a control` output which is a function of the rate of flow of gas through `the conduit 41. VYThis output is applied either, as indicated by dashed line 44, to an actuating or'. settable element of the speed controller 19 or, as indicated by dashed line 45, to an actuating or settable element of` theilow controller 15. lIn either event, `the flow controller regulates the relative proportions of catalyst and feed fed to the reactor 10 so as to maintain. a constant ow ofgaseousmatcrial, Vprin-I cipally unreacted feed,:..through the conduit41.. De pending upon the'settingof controller 42, the. process can be controlled to maintain a minimum amount of unreacted material inthe reactor eluent., Inanyevent,

corporatin'g a valve 14. Thisl valve is `under the control .i

a constant throughput is maintained through thesystem.

Thus, assuming that the ow controller 42 isV- connected to speed controller -1` 9y andvnotfto flow controller 15, the rate of ow offeed'to thereactor can be maintained substantially constant;` 1-

. fl L.'

l.In jsuch instance, 4theoutp ut .:o\f the flow controller 15.1V can be V advantageously utilized. as indicated .by line 15 to set a temperature'recorder. controller -vvhich has a sensing element 15b in 'theeactorandfcontrols,agvalve flhis maintains apredete'rmin direlatiorrbetvveen'feed 15C in a coolant outletline31f5d r connected to ai] rate' andlreacto temperaturefn alarm lSg'is-act'uated VPatented- Oct. .13, 1,959

if the reactor temperature rises above a predetermined value. For example, ilow controller 15 can be reset to lower the feed rate if the reactor temperature becomes too high.

Should-the activity of the catalyst decline, the conversion drops, anda greater amount of unreacted material is present in thel line 41 leading from the separation system. Consequently, speed controller 19 is actuated to increase the amount'of catalyst fed to the reactor so that the conversion is restored to its previous level. An increase in activity of the catalyst produces an opposite effect, namely, an increased conversion with resulting diminution in the amount of unreacted material passing through the line 41. This causes the rate of ow of catalyst to bedecreased, and the amount of material converted to be restored to its original level.

Assumingnow that the floW controller 42 is connected to ow controller 15 and not to speed controller 19', catalyst is fed to the reactor at a constant rate. Again, should the activity of the catalyst increase, the conversion is increased, and less unreacted material flows through line 41. As -a result, flow controller 42 resets flow controller to increase the amount of `feed to the reactor and thus restore the predetermined 110W of unreacted material through the conduit 41. Conversely, a decrease in catalyst activity causes an increase in the amount of unreacted material yfed to line 41 with the result that the ow controller 15 is reset to decrease the feed to reactor 10.

It will `further be apparent that other changes in operating variables of the system than catalyst activity will be corrected =by the control system of the invention.

In some cases, in commercial operation, diiculties are encountered due to surging in the separation system. These diiculties are electively eliminated by the pressure controller 34 which regulates the rate of ow through the separator 37 and conduit 41 in such fashion as to maintain constant pressure in the flash chamber 27.

Alternatively, if such surges are present, the effect upon the operation of the control system can be eliminated by integrating or averaging the output of ow controller 42 over a predetermined period of time. Such a System is illustrated by Figure 2 wherein a flow controller 50 is provided which produces an electrical output representative ofthe velocity of ow through the conduit 41. The electrical output of the controller 50 is fed to an integrating circuit 51 which, in turn, produces an electrical output `'responsive to the average output of controller 50 takenover -a predetermined` interval of time. This integrated output is applied to the speed controller 19, or alternatively, to the ow controller 1S of Figure 1, thus providing a very advantageous smoothing action, and eliminating the effect of surges in the separation system upon smooth, continuous operation of the control system. The ilow controllers, integrating circuits, and speed controls described in the foregoing discussion are standard control instruments well known to those skilled in the art of'process control instrumentation.v The details and structure of these instruments per se form no part of the present invention. Suitable ow controllers include those described in Bulletin 427-1 (August 1950) of the Foxboro Company, especially page 17, and those described in Catalog No. 15-13 (1948), especially page 16, of the Brown Instrument Company. An example of a suitable integrating circuit is illustrated in The Electronic Control Handbook, `by Batcher and Moulic, published by Caldwell-Clements Incorporated, New York, 1946, page 219, at paragraph 43. A suitable speed control is illustrated in thesame handbook on page 278, paragraph 'i 32L` lThese 1examplesHilo; `not exhaust the possibilities. Other specific instruments are Ywell known and can be readily: supplied or substituted by those skilled in the art. Although, as indicated, the control method and apparatus are applicable generally to liquid phase reactions involving a' .granularA catalyst, they have special importance and application to polymerization reactions of 1- olefins containing no more than 8 carbon atoms and having no branching nearer the double bond than the 4 position. As an example of a specific process of this type, can 1be mentioned the polymerization of ethylene with a chromium oxide catalyst supported on silica, alumina, or silica-alumina. In this system, the feed is ethylene of purity containing small quantities of impurities such as methane, ethane or carbon dioxide. This material is fed at a rate of 14.6 cubic feet per hour to the reactor together with one gallon per hour of isooctane diluent introduced through line 20 together with sufficient catalyst to maintain 0.1 to 0.5, specifically 0.3 weight percent catalyst in the eflluent. The reactor was operated at a temperature of 285 F. and a pressure of 500 pounds per square inch gage, the eluent being heated to a temperature of 325 F. by the heater 25. The reactor efuent contains 0.3 weight percent catalyst, 6.5 weight percent polyethylene, 6.5% ethylene, 0.7% light gaseous impurities yand 86.0% solvent. A pressure of pounds per square inch gage is maintained in the flash chamber 27 and a pressure of 90 pounds per square inch gage is maintained in the separator 37, the condensate entering the separator 37 at a temperature of 100 F. A back pressure is maintained on the heater 25 in any suitable manner, lfor example, by a pressure regulator connected to the valve in line 26 just upstream of the flash chamber 27.

Under these conditions, the bottoms product of the flash chamber contains 0.3% catalyst, 6.9% polymer, 1.1% ethylene, 0.1% light gaseous impurities, and 91.6% solvent. Offgas was withdrawn from the separator 37 at a rate of 6.7 standard cubic feet per hour which was the control p oint of iow controller 42. This gas had a composition of 81% ethylene, 10% solvent and 9% light gaseous impurities. The offgas rate was readily maintained at 6.6 to 6.8 standard cubic Ifeet per hour through the operation of the control system either when connected to the catalyst valve 18 or the flow control valve 14 on the ethylene feed line, and very smooth operation of the process was obtained, as contrasted with a considerable variation in oifgas rate, and considerable Iloss of ethylene when the control system of the invention was not employed.

It will be understood, of course, that the invention is not to -be limited to the specific example given, even in its very advantageous application to the control of the polymerization of l-olens having no more than 8 carbon atoms with no branching nearer the double bond than the four position. For example, the polymerization of oleins such as propylene, l-octene, can be advantageously controlled by the system of this invention, and in some cases the polymerization of diolefns or conjugated diole fins of no more than 8 carbon atoms can -be advantageously controlled.

Further, various polymerization catalysts can be used, and various materials, such as thoria and zirconia are suitable as supports and have catalytic activity. Additional promoters such as zinc oxide, magnesium oxide, 'strontium oxide, and the like can be employed. Further, various solvents can be utilized provided that they do not impair the activity of the catalyst. Thus, aliphatic and alicyclic hydrocarbons of 3 to 12 carbon atoms preferably 5 to 12 car-bon atoms per molecule are suitable, specifically propane, normal butane, cyclohexane, methylcyclohexane and isooctane.

Finally, the reaction temperatures, pressures and feed rates can be varied, a range of to 450 -F. being used for the recited 'l-olens generally with a preferred range for propylene of 150 to 250 F. and for ethylene of 275 to 375 F., with a pressure varying from atmospheric to 700V pounds per square inch gage 'or higher.

Referring now to Figure A3, I have shown'a modified control system as, applied to avreactorofthe socalled gas cap type. In this figure, parts corresponding to those of -Figure '-1-'E are "indicatedf by like reference numerals.`

-In` thislireactor, apredetermined'liquidl level 'is maintained fbyla level controller 60 i having 'a sensing element `61,within the reactor 10,-'this controllerbeingconnected to the motor valve ZZ'in the effluenti withdrawal line 2,1. Thus-,f the liquidfwithinf the reactor is maintained at a predetermined level andthere is a gas space above thisy liquid level. Also, a pressure-recorder controller 62 has a' sensing element-63 within the gasy phase of the reactor, and this pressure controller Ais `connectedso-'asv to set the ilowrecorder controller 15. T-hus, the rate of iiow of ethylene -into theli'eactor is regulated so asto maintain -a constant predetermined pressure therein. Otherwise, with this modification, the operation is as described in Figure 1 in that the controller 19 regulating the rate of catalyst iiow is connected' by4 connection 44to the ilow recorder, not shown, in the-eliluent 'line from the liash system, as previously described in connection with Figure l.'

While the invention has been described in connection with present, preferred lembodiments thereof, itis to be understood that this description is illustrative only and is not intended to limit the invention.`

Ipclaim: j

l.` The method of 'controlling' the:polyrr'ieirizationI of a l-olefin having "no morethan 8"carbon atomswith no ybranching nearer the dtmblehbond thanthe-four position, wherein said l-'ole'niis' polymerizedin liquid phase in a reaction Vzone in' the presence of a` granular polymerization catalyst continuously AfedtoA said reaction zone, 1 and the effluent from the reaction zone is separated, yin a separation zone, intoe-apolymer-fraction anda `fraction containing unreacted 1-oleiin, thestepswhich comprise measlruring the-rate of 'iiowof-'the 5'separated unreactedy component from the separation zone, producing a""con1:rolioutput ywhich varies with the rate of liow of unreactedl-olefin-'from the separation zone, and varying Athe ratioY of catalyst to feed in accordance with the magnitude of said'icontrol output, thereby tov-maintain constant the amount of` unreacted feed present in said eiiluent.

i 2,5 The method of controlling the polymerization of a 1- olefin` having no morey than' `8 'carbon atoms with Vno branching nearer the double bond thanithefour position, wherein said l-olelinis polymerized in liquid phase' in fa reaction zone in the presenceofla granularpolymerization catalystcontinuouslyzfed to 1lsaid reaction'zone,` and theeiliuent from the reaction zone is separated, in a separation zone, into a polymer fraction and `a`-fraction containing" 'unreacted` l-ol'en, the steps which comprise measuring the rate oftflow'ofthe separated unreacted component from the separation` zone, producing a control output which va'rieswith thev rate offlow ofunreacted 'l-olein lfrom said' separation zone, and controlling the rateof ilow offeed to said reaction zone in accordance withtheimagnitudepf said'control output while maintaining the rate of'llow of catalyst to said reaction zone at la lsubstantially) `constant 'value,` therebyl to maintain constant 'the-amount ofunreacted lfeedfinV said eflluent.

A3.- 'Ihe method off-controllingthe-polymerization of a lolefin having;no,-more,thanqs carbon atoms with no Ibranching nearer fthe doublebondthan the four position, wherein` said?` 1-oleir1wis polymerizediin 'liquid phase lin a [reaction zone in the presence of a granular polymerization catalystfcontinuously fed at'osaidf reactionzone, and J y the eflluent from thereaction zone iswseparated, in a y separation zone, into a polymer fraction "and a fraction containing unreacted l-olen, thei steps' whichifcomprise measuring the rate-of- -iiowof 'thef separated fun-reacted corriponentfrom-theseparation?zorg-producing4 `afcontrol l-oliin jfl-'oni said sepa-ration zone; and controlling fthe ratelofowlof catalyst-to said reaction" zone in accord- `ance with the magnitude of said control output while maintaining the rate of Afeed to said reaction at a su-b- 6 stantially constant valira-therebyr to maintain constant the amount of un'reacted feed present in 'said 'eiuent 4. The method of controlling the polymerization of a lolefin having no more than 8 carbon atoms with no branching nearer the dou-ble bond than the Afour position,

of said control output, thereby to maintain constantthe amount of unreacted feed present in saidV eluent, and maintaining a substantially constant pressure in said separation zone to smooth out the flow of umeacted l`olen therefrom.

5 The method Vof claim 4l wherein the Vreaction-zone is maintained liquid full. Y

6. The method of claim 1 wherein the `reaction zone is partially filled with liquid and a gaseous phase occupies the remainder Y of the reaction'zone above the liquid phase therein.

7. The method of controlling the polymerization of afl- ,olen' having no more than 8 carbon; atoms with no branchingV nearer the double bond than the four position, wherein -saidl-oleiin is polymerized inl -liquid phase in a reaction zone in the presence of a granular` polymerization catalyst continuously `fed to said reaction 'z one, and the ellluent from the reaction zone is` separated, in a separation zone, lintoa'polymerfraction and a fraction containing unreacted g l-olefin,l thev steps whichV comprise measuring the rate of ilow of the separated unreacted component xfrom the separation zone, producing a control outputwhich lvaries with therate of diow` of unreacte'd l-oleiin from said separation zone, varying the ratio of catalyst to feed in -accordance with the magnitude of said control output, thereby to maintain constant the amount of unreacted feed present in said eiuent, and` integrating said control output to produce an output which varies in accordance with the average value ofthe rate of flow of said unreacted l-olen taken overa predetermined time interval. v v

8,. 'Ihe process of claim lgwherein the l-oleiinis ethylene andthe catalystis chromium oxide supported yon a carrier selected from the group consisting of silica, alumina and silica-alumina.

The method of controllingthe polymerizationofa -l-olen `having no more than Scarbon atoms with nov measuring'the rate of fflw of` said vapor4 through said Y overhead conduiuproducing a control output proportion-1 al to the rateofdiow of'vapor through the said overhead Conduit, and ontrollingfthe :ratio of catalyst and 1-016@ fed to said reaction zone in accordance with the maghi-i tude of said control output, thereby 'to KJmaintain consaidreaction zone.

10. The method of controlling the polymerization of a l-olelin having no more than 8 carbon atoms with no branching nearer the double bond than the four position, wherein said l-olen is fed to a reaction zone and polymerized in the presenceA of a granular polymerization catalyst 4fed to the reaction zone in a slurry with a hydrocarbon solvent, the eiuent is introduced to a ash separation Zone wherein a liquid polymer-containing stream is separated `from a gaseous stream containing unreacted 1olen, the gaseousstream is partially condensed and fed to a liquid-vapor separation zone, the liquid from said separator zone being returnedto said ash zone and the vapor from said separator zone being withdrawn through an overhead conduit, measuring the rate of ow of said vapor through said overhead conduit, producing a control output directly proportional to the rate of flow of vapor through said overhead conduit, and controlling the rate of flow of said 1o1en to the reaction zone in accordance with the magnitude of said control output while maintaining the rate of catalyst addition at a substantially constant value, thereby to maintain constant the amount of unreacted l-olefn present in the eiuent from said reaction zone.

11. In a process for controlling the polymerization of ethylene wherein ethylene is introduced into a reaction zone and therein contacted with a granular chromium oxide-containing catalyst dispersed in a slurry of hydrocarbon material selected from the class consisting of parans and cycloparaflins, the eluent from the reaction zone is heated and passed to a flash zone wherein a polyethylene stream is separated from a vaporous stream containing unreacted ethylene, said vaporous stream being partially condensed and fed to a liquid-vapor separation zone, the liquid 'from which is returned to the ilash zone and the vapor from which is withdrawn through au outlet conduit, the steps which comprise measuring the rate of flow of said vapor through said outlet conduit, producing a control output proportional to the rate of ow of gas through said outlet conduit, and varying the amount of catalyst `fed to said react-ion zone in accordance with the magnitude of said control output while maintaining a substantially constant rate of ow of ethylene to the reaction zone, thereby to maintain constant the amount of unreacted ethylene present in the efuent from said reaction zone.

12. In a process for controlling the polymerization of ethylene wherein ethylene is introduced into a reaction zone and therein contacted with a granular chromium oxide-containing catalyst dispersed in a slurry of hydrocarbon :material selected from the class consisting of parains and cycloparains, the eiuent from the reaction zone is heated and passed to a ash zone wherein a polyethylene stream is separated from a vaporous'stream containing unreacted ethylene, said vaporous stream being partially condensed and fed to a liquid-vapor separation zone, the liquid from which is returned to the flash zone and the vapor from which is withdrawn through an outlet conduit, the steps which comprise measuring the rate of ow of said vapor through said outlet conduit, produoing a control output proportional to the rate of flow of gas through said outlet conduit, maintaining a substantially constant pressure in said reaction zone and said ash zone, integrating said controlroutput to produce an electrical voltage proportional to the average value of ow through said outlet conduit taken over `a predetermined interval of time and varying the amount of catalyst lfed to said reaction zone in raccordance Iwith the magnitude of said integrated control output while maintaining a substantially constant rate of flow of ethylene to the reaction zone, thereby to maintain constant the amount of unreacted ethylene present in the effluent from said reaction zone. Y

l13. A control system for a polymerization plant including a reactor, a feed line connected to said reactor, a rate of flow controller connected to said feed line hav` ing a control element, a catalyst introduction line connected to said reactor having a valve thereincontrolling the introduction of granular catalyst to said reactor, a control element connected to said valve and controlling the operation thereof, a dlash cham-ber, an efuent line connecting said reactor to said flash chamber, a separator vessel, a line including a condenser connecting the top of said flash chamber to said separator vessel, an overhead conduit connected to said separator vessel, a rate of ow controller connected in said overhead conduit and producing an output representative of the flow therethrough, and means applying said output to one of said control elements.

14. The method of controlling the polymerization of a l-olen having no more than 8 carbon atoms with no branching nearer the double bond than the four position, wherein said l-olefn is polymerized in liquid phase in a reaction zone in the presence of a granular polymerization catalyst continuously `fed to said reaction zone, and the efuent from the reaction zone is separated, in a separation zone, into a polymer fraction and a fraction containing unreacted l-olen, the steps which comprise measuring the rate of ow of the latter-mentioned fraction from said separation zone, producing a control output which varies with the rate of tlow of unreacted l-olefin from the separation zone, controlling the ratio of catalyst and l-olen fed to said reaction zone in accordance with the magnitude of said control output, passing a cooling medium in indirect heat exchange relationship with the reaction zone, and regulating the amount of cooling medium thus passing in indirect heat exchange relationship to maintain the reactor temperature at a preassigned value.

15. A control system for a polymerization plant including a reactor, a feed line connected to said reactor, a rate of ow controller connected to said feed line having a control element, a catalyst introduction line connected to said reactor and having a valve therein controlling the introduction of catalyst into said reactor, a control element connected to said valve and controlling the operation thereof, a ash chamber, an effluent line connecting said reactor to said flash chamber, a conduit yfor withdrawing reaction product from said dlash chamber, conduit means in communication` with a vapor space 'in said flash chamber, a rate of ow controller connected to the last-mentioned conduit means and producing an output representative of the flow therethrough, and means applying said output to one of said control elements.

16. In the process of continuously polymerizing polymerizable monomers in the presence of a polymerization catalyst fed continuously in the polymerization zone wherein the reactor eiuent comprises ploymer and unreacted monomers, the improvement comprising separating said effluent, in a separation zone, into -a polymer fraction and a fraction containing said unreacted monomers, measuring the rate of iiow of the separated unreacted monomers vfrom the separation zone, producinga control outputwhich varies with the rate of ow of unreacted monomers from the separation zone, and varying the ratio of catalyst to feed lin accordance with the magnitude of said control output thereby maintaining constant the amount of unreacted feed present in said eluent.

References Cited in the tile of this patent UNITED YSTATES PATENTS 2,373,888 Hachmuth Apr. 17, 1945 2,462,995 Ritzmann Mar. 1, 1949 2,518,307 Groebe Aug. 8, 1950 2,606,940 Bailey et al Aug. 12, 1952 2,731,452 Field et al. Ian. 17, 1956 2,792,501 Barton May 14, 1957 AFC K a 

1. THE METHOD OF CONTROLLING THE POLYMERIZATION OF A 1-OLEFIN HAVING NO MORE THAN 8 CARBON ATOMS WITH NO BRANCHING NEARER THAN THE DOUBLE BOND THAN THE FOUR POSITION, WHEREIN SAID 1-OLEFIN IS POLYMERIZED IN LIQUID PHASE IN A REACTION ZONE IN THE PRESENCE OF A GRANULAR POLYMERIZATION CATALYST CONTINUOUSLY FED TO SAID REACTION ZONE, AND THE EFFLUENT FROM THE REACTION ZONE IS SEPARATED, IN A SEPARATION ZONE, INTO A POLYMER FRACTION AND A FRACTION CON- 